In order to enhance the competitiveness of mobile networks in the future, the 3rd Generation Partnership Project (3GPP) is focusing on the System Architecture Evolution (SAE) that integrates multiple networks for the next stage of development. In an SAE network architecture shown in FIG. 1, the user may access the Evolved Packet Core through a 3GPP access system or through a non-3GPP access system. The 3GPP access system is a General Packet Radio Service (GPRS), Universal Mobile Telephone System (UMTS), or SAE. The non-3GPP access system is a Wireless Local Area Network (WLAN), Worldwide Interoperability for Microwave Access (WiMAX) network, Code Division Multiple Access (CDMA) system, or CDMA2000.
As shown in FIG. 1, the Evolved Packet Core includes three logic function modules: Mobility Management Entity (MME)/User Plane Entity (UPE), 3GPP anchor, and SAE anchor. The MME is responsible for mobility management on the control plane, including: managing user contexts and mobile states, allocating Temporary Mobile Subscriber Identifiers (TMSIs), and performing security functions. The UPE initiates paging for downlink data in the idle state, and manages and stores the parameters over the Internet Protocol (IP) and the routing information in the network. The 3GPP anchor is an anchor between the 2G/3G and the Long Term Evolution (LTE) access system, and the SAE anchor serves as a user-plane anchor between different access systems.
When the 3GPP anchor combines with the SAE anchor into an Inter Access Systems Anchor (IASA) serving as an outbound service anchor of all access technologies in the SAE, the User Equipment (UE) may be connected to the IASA through an Evolved RAN (E-RAN) or MME/UPE. In this case, the UE communicates with the MME/UPE by the Mobility Management (MM)/Session Management (SM) protocol, and the MME/UPE communicates with the IASA by GPRS Tunnel Protocol (GTP). Alternatively, the UE may also be connected to the IASA through a non-3GPP GW, the UE communicates with the non-3GPP Gateway (GW) through a specific radio protocol, and the UE communicates with the IASA by Mobile Internet Protocol (MIP) or IKEv2 Mobility and Multihoming Protocol (MOBIKE).
When the UE moves between the 3GPP access systems, the GTP protocol is used between the Serving GPRS Support Nodes (SGSNs) or used between the SGSN and the MME/UPE to transfer the UE-related information (for example, MM context and Packet Data Protocol (PDP) context) from the previous system to the current system. When the UE moves between non-3GPP access systems, the UE interacts with the IASA through the MIP/MOBIKE protocol.
However, when the UE moves between different types of systems, for example, hands over from a 3GPP access system to a non-3GPP access system, or from a non-3GPP access system to a 3GPP access system, it is very difficult to transfer service information of the UE between the MME/UPE and the non-3GPP GW. Therefore, when selecting the IASA, the Domain Name System (DNS) needs to be resolved again, which increases the time of the UE handover. Moreover, the UE may be anchored onto different IASAs when handing over to the current access system. Therefore, for the UE with an underway service, namely, the UE with an active service, the service tends to be interrupted. For example, when the UE with an active service hands over from a non-3GPP access system to a 3GPP access system, the UE needs to perform a new PDP context activation process at the 3GPP access system. When the UE activates the PDP context at the 3GPP access system, the MME/UPE performs DNS resolution for the Access Point Name (APN) provided by the UE, and selects a result as the IASA of this service. This mechanism is unable to ensure that the selected IASA is the IASA used when the UE performs the service at the non-3GPP access system. If the two IASAs are different, the underway service of the UE may be interrupted.